1. FIELD OF THE INVENTION:
The present invention relates to a floppy disk. More particularly, it relates to a disk cartridge using a hard casing instead of a thin jacket.
2. DESCRIPTION OF THE PRIOR ART
A floppy disk has widely been used as an exchangeable information storage medium which can be fitted to a driving unit (a magnetically recording and reproducing device) and removed from it for storage or transportation in the same manner as a magnetic tape cassette and a disk pack. Eight-inch and five-inch floppy disks have been commonly used. For such floppy disks, a thin flexible jacket made of vinyl chloride has been used as a casing to protect a magnetic disk. In consideration that the thin flexible jacket type floppy disk is insufficient to protect the magnetic disk, there has been proposed a disk cartridge in which a thick, hardly deformable, strong hard case is used and lining sheets are attached to the inner surfaces of the hard casing to receive a magnetic disk in a rotatable manner.
FIG. 1 is a perspective view showing the outline of the above-mentioned disk cartridge and FIG. 2 is a longitudinal cross-sectional view of the disk cartridge.
In the Figures, a reference numeral 10 designates an upper hard casing, a numeral 12 designates a lower hard casing and a numeral 14 designates a shutter which covers a window for insertion of a magnetic head (not shown) to protect a magnetic disk 16 recieved in the disk cartridge when it is in non-use. The magnetic disk 16 has an annular base portion which is coated with magnetic material on both its surfaces and is provided with a hub 20 at the central portion. The hub 20 includes a central circular projection 22 projecting downward as the major part and an annular part 24 for connecting the magnetic disk 16, the annular part 24 extending outwardly from the outer peripheral edge of the circular projection. The circular projection 22 of the hub faces a magnetic-disk driving window 26 formed in the lower hard casing 12 to substantially cover the window 26 when the disk cartridge is not used, whereby in addition to provision of the shutter 14, protection of the magnetic disk 16 received in the disk cartridge can be easy and operation of the cartridge is simple to thereby increase reliability.
A reference numeral 28 designates a driving pin upwardly extending from a mounting table 30 of the driving unit. The central opening 32 of the hub 20 is fitted to the driving pin in the vicinity of the top end of it, which reaches a bearing part 34 at the center of the upper hard casing 10. Accordingly, there is no magnetic-disk driving window in the upper hard casing 10 and the top end of the driving pin 28 merely comes in contact with the central bearing part 34 provided in the upper hard casing. A supporting member 36 for the hub which may be in an annular form is mounted on the mounting table 30 of the driving unit. The upper surface of the supporting member 36 is in contact with the hub 20 so that it supports the hub when rotated. The supporting member 36 has a central opening 38 through which the driving pin 28 extends with an air gap between the cylindrical surface and the inner wall of the central opening 38. A magnet 40 which may be a ringed magnet is provided around the supporting member 36 for supporting the rotation of the hub 20. The magnet 40 is able to attract the hub 20, which may be a metal hub of a ferromagnetic substance such as stainless steel.
FIG. 3 is an enlarged cross-sectional view showing the conventional hub as in FIG. 2. As apparent from FIG. 3, a contacting surface of the hub which is in contact with the supporting member 36, namely the lower surface of the circular projection 22 of the hub, is slightly raised from the outer radially peripheral portion of the circular projection 22 toward the central opening 32 of the hub 20 in which the driving pin 28 is inserted.
When the raised lower surface is formed, it is necessary that a curved corner portion 31 is formed at a portion to be bent of the contacting surface of the hub. It is difficult to form corner portion without a curvature when the contacting surface of the hub is bent. Formation of the curved corner portion 31, however, deteriorates flatness in the contacting surface (reference surface) of the hub due to a stamping operation. Therefore, the hub 20 can not stably be supported by the supporting member 36 when the hub is rotated. Particularly, there takes place oscillation of the hub 20 in the vertical direction as shown by the arrow mark X even when the metallic hub 20 is attracted by the magnet 40, on account of which contact between the magnetic head (not shown) and the magnetic disk 16 becomes worse, whereby performance of the disk cartridge decreases.